1. Field of the Invention
The present invention relates to a communication system for making a plurality of communication apparatus send and receive information through electric power line. Furthermore, the present invention relates to a communication apparatus, a communication system, a wire harness and a communication method for implementing stable high-speed communication.
2. Description of Related Art
It is recently known in several fields to utilize a system having many communication apparatuses, in which each communication apparatus is provided with a certain function and connected with other communication apparatuses in order to perform many operations through the data exchange between many communication apparatuses. For example, it is known in a field of local area network (LAN) mounted on a motor vehicle to utilize electronic control units (ECUs) as the communication apparatuses, to make each ECU perform a certain operation and to exchange data between the ECUs, in order to provide many functions to be implemented by a system.
A number and a type are increased of the communication apparatuses included in a communication system, proportionally to a specializing degree of the function provided to each communication apparatus, as well as an increasing degree of the functions performed by each communication apparatus. Furthermore, a number is also increased of communication lines for connecting communication apparatuses with each other. Moreover, it is required to send and to receive large amounts of data in high-speed, proportionally to an increasing degree of data amount sent and received in the communication system.
Recently, some attention is drawn to the Power Line Communication method (PLC method) for implementing communications with utilizing communication carrier wave superimposed on the existing electric power line, which is proposed to be applied to an on-vehicle LAN (e.g., Patent Document 1).
Patent Document 2 proposes a signaling method utilizing a new modulating approach for implementing communications among a plurality of apparatuses through DC electric power line and for implementing efficient and high-speed signal transmission over a plurality of frequency channels. This signaling method modulates the carrier wave by an approach of Binary Phase-Shift Keying (BPSK), Quaternary Phase-Shift Keying (QPSK), Amplitude Modulation (AM), Frequency Modulation (FM), Code Division Multiple Access (CDMA) or the like, and modifies the carrier wave by an approach of phase shift, amplitude shift, frequency shift or the like.
In the case that a plurality of communication apparatuses performs data transmission through a connection line (communication line or electric power line), arbitration is required for preventing a data sending operation of communication apparatuse from conflicting with another data sending operation of another communication apparatus. For example, in the control area network (CAN), only one communication apparatus can send data among a plurality of communication apparatuses connected with each other through a communication line, and the other communication apparatuses are controlled to wait until said one communication apparatus has completed the data sending operation. When plural communication apparatuses try to send data concurrently, it causes conflicts of sending data. Thus, each communication apparatus performs the arbitration with the other communication apparatuses and then sends the data.
The data sent in the CAN protocol includes an identifier (ID) that is assigned to each king of information included in the sent data for identifying said each kind of information. The arbitration of sending data is performed with utilizing the ID as the information representing priority, and the data field including the ID of the sent data is called the arbitration field. For example, a smaller number is assigned as the ID to higher importance information, such as status information about engine of a vehicle, and a larger number is assigned as the ID to lower importance information.
The CAN utilizes two-wire bus for sending and receiving the operation signals, and utilizes two types of bus values: a dominant value corresponding to data “0” and a recessive value corresponding to data “1”. When one communication apparatus sends a dominant value in the case that plural communication apparatuses are sending data through the bus standardized by the CAN, the bus value becomes to be the dominant value. During the data sending operation, each communication apparatus performs bitwise comparison between a value in the arbitration field of the sent data and the bus value. In the case that the bus value of the communication line is the dominant value corresponding to data “0” at the time when the communication apparatus sends the recessive value corresponding to data “1”, the communication apparatus stops sending the data and then performs the receiving operation. Thus, it is possible to preferably send data whose ID is smaller number, and to perform the arbitration of data sending operation among the plurality of communication apparatuses.    [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-67421    [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-124902